Electrochemical Practice Exam

In an electrochemical cell, the electromotive force (e.m.f.) is influenced by the concentration of the reactants and products involved in the redox reactions. The given cell involves magnesium and iron in their ionic and solid states, respectively.

According to the Nernst equation, the e.m.f. of a cell is related to the concentrations of the ionic species involved. Specifically, for the reduction half-reaction of iron, a higher concentration of Fe2+ would increase the e.m.f. Conversely, for magnesium, which acts as the anode, a lower concentration of Mg2+ typically promotes the oxidation of magnesium metal, allowing it to release electrons more readily.

When the concentration of Mg2+ decreases, it actually shifts the equilibrium of the oxidation reaction towards the production of more magnesium ions from the magnesium metal. This increase in the tendency for magnesium to oxidize results in a greater potential difference, which effectively increases the e.m.f. of the cell.

Thus, decreasing the concentration of Mg2+ enhances the overall e.m.f. due to the increased tendency for magnesium to oxidize and provide electrons, demonstrating the cell's ability to do work more efficiently in that condition. This is in line with the principle that lowering the concentration